Beam Scanning UHF RFID Reader Antenna with High Gain and Wide Axial Ratio Beamwidth

A novel ultra-high-frequency (UHF) RFID reader antenna is proposed, designed and measured. The proposed antenna is capable of 2-dimensional (2D) beam-scanning from 0º to 360º in the azimuth plane, and 0º to 40º in the zenith plane. The minima of the antenna's axial ratio (AR) follows its gain maxima during beam-scanning, resulting in an equivalent 3 dB AR beamwidth of over 136º for every phi cut. Moreover, the antenna's AR can be easily modified without affecting other parameters. It is shown experimentally that the antenna's 2D beam-scanning ability and the improved AR performance lead to better tag-reading results, improving the percentage of missing tags by up to 21.6% compared to a standard antenna which has a degraded AR and only supports 1D beam-scanning. In addition, the antenna needs no matching network and has a -10 dB return loss bandwidth from 860 MHz to 880 MHz.This work was supported by EPSRC EP /S-19405/1 Channel Optimised Distributed Passive Sensor Network

A UHF RFID Reader Antenna with Tunable Axial Ratio and Fixed Beamwidth

A novel ultra-high-frequency (UHF) RFID reader antenna is proposed. The antenna has a unique property as being able to change its axial ratio (AR) without affecting its gain, beamwidth or impedance matching performance, enabling the isolated study of the effect of different axial ratios in RFID tag reading.This work was supported by EPSRC EP /S-19405/1 Channel Optimised Distributed Passive Sensor Networks

A 3D Ray-tracing Model for UHF RFID

In this work, a 3-dimensional (3D) ray-tracing model is proposed. The model is specifically tailored for RFID applications by taking into account some of its unique characteristics. The proposed model can give accurate power predictions and is suitable for indoor RFID systems operating with low fade margins. The model has been verified by comparison with Method of Moments (MoM) and practical measurements. It is shown to achieve a high accuracy with significantly less computational complexity than MoM. An example application of the model is presented comparing the performance of two antennas with similar beam patterns but different axial ratio. The predicted tag detection rates (63% and 50%) are in good agreement with the experimental data (65% and 55%), showing the accuracy of the model and its improvement over previous models which are not able to handle axial ratio as accurately.This work was supported by EPSRC EP /S-19405/1 Channel Optimised Distributed Passive Sensor Networks

DISTRIBUTED PHASED ARRAY ANTENNAS IN WIDE AREA RFID

Ultra High Frequency (UHF) Radio Frequency Identification (RFID) has gained importance over the past two decades in many applications such as stock management, asset tracking and access control. For wide area applications, Distributed Antenna Systems (DAS) have been used to obtain good coverage with few antennas by making use of multiple spatially distributed antennas and phase dithering. This implements a far-field beamforming that maximises the instantaneous power at a tag. Separately, phased array antennas have also been used to increase the read range by increasing the effective field of view of an antenna and overcoming multipath fading through beam steering. This dissertation explores a combination of both approaches to improve RFID read ranges in wide interrogation zones. Distributed antenna arrays are explored in the context of delivering high tag detection probabilities in a multi-cell RFID system, while maximising inter-antenna separations. A Distributed Antenna Array System (DAAS) is designed and shown to be capable of providing comparable performance to a fixed DAS system with fewer antennas. The properties of the system are further studied and its upper performance limit is explored by modelling a hypothetical perfectly steerable antenna array. The concept of using perfectly steerable arrays is further explored to propose a cell-less RFID system, in which cell allocation in wide area RFID is replaced with a tag location-based interrogation requiring the global reader antenna population to be used for interrogation of all tags, leading to significant potential increases in inter-antenna separation, and consequently good coverage with fewer antennas. It is also argued that this system leads to the avoidance of complex reader anti-collision policies, since only a single central reader is now required. Finally, the design of a wide-scan-angle antenna array is presented as a compromise solution for perfectly steerable antennas, whist still keeping the desired property of being flat panel. A 3D RFID multi-antenna model is presented and used for simulating and analysing the various described systems and for system planning

Dielectric Resonator Antenna Mounted on Cylindrical Ground Plane for Handheld RFID Reader at 5.8 GHz

Dielectric resonator antenna (DRA) mounted on cylindrical ground plane is investigated for handheld RFID reader applications at 5.8 GHz. The simplicity of the structure makes it practical in terms of cost, space, and ease of fabrication. The radiation characteristics of the antenna in free space and in the presence of a proposed compact reader device model and human hand are calculated. The antenna is circularly polarized and exhibits peak gain of 7.62 dB at 5.8 GHz with high front to back ratio of 15.5 dB. Using the same reader device model, a sequentially feeding 2×2 DRA array mounted on the same cylindrical ground plane is used for RFID reader antenna at 5.8 GHz. The array introduces high gain of 9.36 dB at 5.8 GHz with high front to back ratio of 10.48 dB. The 2×2 DRA array elements exhibit circular polarization over a frequency band of 1.1 GHz. The axial ratio is 1.1 dB at 5.8 GHz. The proposed reader model is simple and has a small size compared with that in the case of planar ground plane. The results are calculated using the finite element method (FEM) and compared with that calculated using the finite integral technique (FIT)

AN INVESTIGATION OF NOVEL UHF MICROSTRIP FRACTAL PATCH ANTENNAE FOR AN RFID DOORWAY READER SYSTEM

The applications of Radio Frequency Identification (RFID) technology has expanded drastically after the arrival of data revolution and coming age of human-free industry: Industry 4.0. The focus has been reduction of installation costs by developing plug and play systems when transitioning from traditional manual-scan systems to fully automated systems with improved efficiency. The main contributor to efficiency of an RFID system is the reader antenna. Microstrip patch antennae are found to be most suitable for RFID applications. Miniaturisation of the antenna without compromising its efficiency has been one of the central concerns in the last few decades. For fixed reader RFID antennae, maintaining enough gain while having the ability to read tags moving in any orientation and speed as well as blindspots when clustered together have been major challenges in the industry. The work proposed in this thesis aims to design miniaturised novel modified fractal antennae suitable for an RFID doorway reader system, operating at UK’s RFID UHF band, 870MHz. The work proposed combines novel miniaturising and gain enhancement techniques to meet desired requirements. Fractal patterns are used to increase the electrical length of the antenna while maintaining its physical size and obtain multiband behaviour thus reading tags slightly off-tuned with the help of RFID reader’s Frequency hopping technique. Antennae are made on high dielectric constant substrates, RF60A for further miniaturisation. Several geometry techniques including copper wall construction and 90 degree delayed two port feeders are used for gain enhancement, narrow beamwidth and circular polarisation. CST Microwave Studio Suite simulations demonstrate that a commercially available directivity (5dBi) compared to market research and published research papers have been achieved. RFID testing on manufactured prototypes demonstrated that antenna designs are suitable for a fully automated doorway reader system to obtain 100% detection efficiency with precise manufacturing and fine tuning

Antenna Array Designs For Directional Wireless Communicatoin

Ph.D. Thesis. University of Hawaiʻi at Mānoa 2018

A comprehensive survey of "metamaterial transmission-line based antennas: design, challenges, and applications"

In this review paper, a comprehensive study on the concept, theory, and applications of composite right/left-handed transmission lines (CRLH-TLs) by considering their use in antenna system designs have been provided. It is shown that CRLH-TLs with negative permittivity (ε < 0) and negative permeability (μ < 0) have unique properties that do not occur naturally. Therefore, they are referred to as artificial structures called "metamaterials". These artificial structures include series left-handed (LH) capacitances (CL), shunt LH inductances (LL), series right-handed (RH) inductances (LR), and shunt RH capacitances (CR) that are realized by slots or interdigital capacitors, stubs or via-holes, unwanted current flowing on the surface, and gap distance between the surface and ground-plane, respectively. In the most cases, it is also shown that structures based on CRLH metamaterial-TLs are superior than their conventional alternatives, since they have smaller dimensions, lower-profile, wider bandwidth, better radiation patterns, higher gain and efficiency, which make them easier and more cost-effective to manufacture and mass produce. Hence, a broad range of metamaterial-based design possibilities are introduced to highlight the improvement of the performance parameters that are rare and not often discussed in available literature. Therefore, this survey provides a wide overview of key early-stage concepts of metematerial-based designs as a thorough reference for specialist antennas and microwave circuits designers. To analyze the critical features of metamaterial theory and concept, several examples are used. Comparisons on the basis of physical size, bandwidth, materials, gain, efficiency, and radiation patterns are made for all the examples that are based on CRLH metamaterial-TLs. As revealed in all the metematerial design examples, foot-print area decrement is an important issue of study that have a strong impact for the enlargement of the next generation wireless communication systems